By a simple, efficient procedure which is termed "Methanol profix-Acid extraction", basic chromatin protein was isolated from an archaebacterium Sulfosphaerellus thermoacidophilum successfully. Both SDS-PAGE and AUT-PAGE comparison of the protein with histone isolated by the same procedure from calf thymus showed that it contained three major fractions. Like basic chromatin proteins of other archaebacteria reported previously, the molecular weights of the three fractions, which are about 7 200, 8 500 and 9 800 respectively, are all less than that of calf thymus H4(MW 11 282). And they can be stained by Azocarmin G solution (pH7), which specially stains basic proteins such as histone.